ATM (Asynchronous Transfer Mode) is a network technology for both local area networks (LANs) and wide area networks (WANs) that supports real-time voice and video as well as data. The topology uses switches that establish a logical circuit from communication end to end, which guarantees a quality of service for transmissions. However, unlike telephone switches that dedicate circuits end to end, unused bandwidth in ATM's logical circuits can be appropriated whenever available. For example, idle bandwidth in a videoconference circuit can be used to transfer data.
ATM works by transmitting all traffic using fixed-length, 53-byte, cells. This fixed unit allows very fast switches to be built, because it is much faster to process a known packet size than variable length packets. The small ATM packet also ensures that voice and video can be inserted into the stream often enough for real-time transmission.
The ability to specify a quality of service is one of ATM's most important features, allowing voice and video to be transmitted smoothly. The following levels of service are available: Constant Bit Rate (CBR) guarantees bandwidth for real-time voice and video; Real-time variable Bit Rate (rt-VBR) supports interactive multimedia that requires minimal delays, and non-real-time variable bit rate (nrt-VBR) is used for bursty transaction traffic; Available Bit Rate (ABR) adjusts bandwidth according to congestion levels for LAN traffic; and Unspecified Bit Rate (UBR) provides a best effort for non-critical data such as file transfers.
An asynchronous transfer mode (ATM) network comprises a layered architecture allowing multiple services like voice, data and video, to be mixed over a network. The network includes an interface to a physical communication medium, and data can be communicated through buffer circuits. Typically, a buffer circuit is provided that can communicate with a predetermined number of communication ports provided through the physical medium, such as sixteen (16). Often, however, the number and priority of ports varies between ATM systems.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for an adjustable ATM buffer and management circuitry.